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Acrosome The Golgi-derived cap that covers the top two-thirds of the sperm nucleus and contains enzymes that facilitate entry of the sperm through the zona pellucida of the oocyte.

Acrosome reaction Changes in the ultrastructure of the sperm head resulting from binding of the outer acrosomal membrane to the zona pellucida which allows dispersal of acrosomal contents.

Activational actions Effects of steroid hormones that stimulate or inhibit activity of neurons in the central nervous system.

Acrosin A trypsin-like enzyme produced by sperm.

Adenohypophysis The anterior lobe of the pituitary gland, consisting of the distal, intermediate, and infundibular portions.

Adnexa The connected parts of an organ or tract.

Adventitia The outer layer of connective tissue covering an organ or blood vessel. It is formed from outside the organ and is not an integral part of the organ as is the serosa.

Allantois The fetal membrane that develops from the hindgut and forms the umbilical cord and placenta in eutherian mammals.

Allantochorion The extra-embryonic membrane that forms when the allantois and chorion fuse.

Alpha-fetoprotein A serum protein produced during the prenatal and early postnatal period in rats. The protein is believed to sequester estradiol, thereby protecting the female rat from the masculinizing effects of this hormone on the brain.

Amnion The extra-embryonic membrane that envelopes the embryo suspended in amniotic fluid.

Ampulla A sac-like dilation of a duct, such as the ductus deferens and oviduct.

Anaphase The stage of mitosis and meiosis during which the chromosomes migrate from the equatorial region toward the poles.

Androgen A class of steroid hormones that stimulate the male accessory sex glands and promotes development of male secondary sex traits (e.g., testosterone).

Androgen-binding protein A protein produced by Sertoli cells that binds and sequesters testosterone in the seminiferous tubule.

Anestrus A prolonged period during which a female is sexually quiescent and does not express estrus.

Anovulatory wave A follicular wave that does not culminate with ovulation.

Anti-Mullerian hormone A peptide produced by developing Sertoli cells that causes regression of the mullerian ducts in males during differentiation of the genital ducts.

Antrum An enclosed or nearly enclosed cavity such as that found in tertiary follicles.

Apoptosis The genetically programmed self-destruction of a cell.

Appetitive behavior Behaviors that bring an individual into contact with the goal; for example, searching for a sexual partner.

Asexual reproduction Reproduction without sex; that is, without the re-combination of genetic material from separate sources.

Assisted reproduction technologies Any technique that assists sexual reproduction; e.g., artificial insemination, in vitro fertilization, or embryo transfer.

Atresia Death of an oocyte accompanied by degeneration of the surrounding follicle.

Autocrine The process whereby a hormone acts on the cell that produces and releases it.

Autopoiesis Literally, the formation of self. The metabolic processes that allow an organism to sustain itself in the presence of a continually changing environment.

Autosomes Any chromosome that is not a sex chromosome.


Basement membrane A layer of connective tissue underlying the base of a layer of epithelial cells. Also known as the lamina propria.

Binding protein Any serum protein that binds a hormone.

Blastocoele The central cavity of the blastocyst.

Blastocyst An early form of the embryo consisting of an inner cell mass with a thin layer of trophoblasts forming the wall of the blastocoele.

Blastomere A cell formed after cleavage of the egg following fertilization. Also known as a cleavage or embryonic cell.

Blood-brain barrier A barrier that restricts passage of solutes from the blood to the cerebrospinal fluid.

Blood-testis barrier A barrier between the interstitial capillaries and the lumen of the seminiferous tubules that restricts passage of solutes from blood to the tubular compartment.

Broad ligament The peritoneal fold that envelopes and suspends the uterus, uterine tubes (oviducts), and ovaries from the walls of the pelvis.

Bruce effect The phenomenon whereby exposure to a novel male induces abortion in newly-mated female rats.

Bulbospongiosus muscle In males, the skeletal muscle located at the bulb of the penis which constricts the pelvic urethra to promote excretion of urine or enhance expulsion of semen after ejaculation.

Bulbourethral gland An accessory sex gland located near the bulbous penis which secretes ejaculatory fluids into the urethra during ejaculation.


Capacitation The process whereby egg-binding proteins on the surface of sperm are unmasked thereby rendering the cell capable of binding to the zona pellucida and undergoing the acrosome reaction.

Capsule A layer of dense connective tissue that envelopes an organ.

Carrying capacity The population that a particular area will sustain without depleting resources.

Caudal Toward the tale.

Centrioles Tubular structures consisting of a wall of nine triplets of microtubules that exist in pairs near the nucleus of a cell.

Centromere The constricted point of a chromosome that serves as the point of attachment to the spindle fiber.

Cerebrospinal fluid The filtrate of blood that is comparable to serum secreted into the ventricles of the brain and which circulates throughout the ventricles and subarachnoid space within the central nervous system.

Chiasmata An intersection between two fibrous bundles. With respect to cytogenetics, the chiasmata is the point at which the chromatids of homologous chromosomes come into contact with each other. Also known as chiasm or chiasma; for example, optic chiasm.

Chorion The outermost fetal membrane consisting of the extraembryonic mesoderm, trophoblast, and villi.

Chromatid One of the two arms (strands) of a chromosome visible when the chromosome condenses during prophase of mitosis and meiosis. The chromatids of a chromosome are joined at the centromere.

Chromosomal sex The complement of sex chromosomes exhibited by males (XY) and females (XX).

Cilia Motile extensions of the surface of a cell. Circannual rhythm A rhythm with a period of approximately 1 year.

Circadian rhythm A rhythm with a period of approximately 24 hours.

Circumventricular organs Chemoreceptors located near the ventricles of the brain and which are outside the blood-brain barrier.

Clitoris The erectile body located at the anterior border of the vulva between the folds of the labia minora.

Compaction The process whereby cells of the morula converge to form a compact morula. At this stage, cells of the embryo are differentiated into those of the inner cell mass and the outer trophectoderm.

Consummatory behavior Behaviors related to completion of a goal.

Corona radiata The single layer of cells (usually columnar) arising from the cumulus oophorus that anchor the zona pellucida in a follicle.

Corpus albicans Literally means white body. The scar tissue remaining on the surface of the ovary following regression of the corpus luteum.

Corpus hemorrhagicum Literally means bloody body. The blood clot that forms on the ruptured follicle following ovulation.

Corpus luteum Literally means yellow body. The endocrine body that develops from the tissue of the ruptured follicle following ovulation.

Cortex The outer portion of an organ separate from the inner medulla.

Cortical reaction Accumulation of secretory vesicles on the surface of the oocyte in response to the fusion of the sperm membrane with the vitelline membrane of the oocyte.

Cotyledon A structure of the fetal placenta supplied with blood vessels and consisting of chorionic villi which attach to a uterine endometrial structure known as the caruncle.

Cranial Toward the head.

Cremaster muscle The skeletal muscle that suspends and retracts the testis.

Cryptorchidism The failure of the testes to descend from the abdominal cavity into the scrotum.

Cumulus oophorus The mass of granulose cells that surround the oocyte.

Cytokinesis The extranuclear changes in the cytosol of a cell during division.

Cytotrophoblast The inner layer of the trophoblast of an embryo. This layer together with the embryonic mesenchyme forms the chorion.


Decidualization The process whereby the mucosal epithelium of the endometrium is transformed into the maternal tissue of the placenta.

Defeminization The loss of feminine features during sexual differentiation.

Delayed implantation Postponement of placentation. This is one of several mechanisms whereby the time of parturition is synchronized with a time of year that is favorable to survival of offspring.

Deviation The process whereby the largest follicle continues to grow and smaller follicles undergo atresia.

Diestrus The postovulatory phase of the estrous cycle during which the corpus luteum is fully developed and functional.

Diploid The normal complement of chromosomes in somatic cells for a given species.

Distal Away from the center of a body or point of origin of a structure.

Dominant follicle The largest follicle of a follicular wave.

Dorsal Referring to the back or upper surface of an animal.

Ductus deferens The duct running from the epididymis of the testis to the pelvic urethra.


Ectoderm The outer layer of cells in an embryo at the stage when the three germ layers (ectoderm, mesoderm, and endoderm) are established.

Efferent ducts Microscopic ducts draining the rete testis and emptying into the head of the epididymis.

Egg-binding protein The protein on the sperm membrane that serves as a ligand for a sperm receptor located on the zona pellucida.

Embryo An organism at an early stage of development. Usually the embryonic stage ends when the species of the organism is recognizable.

Emergence The stage of follicle development during which secondary follicles become tertiary follicles. Endocrine Referring to secretions internally into the blood or extracellular fluid.

Endocrine gland Ductless glands that secrete products into the extracellular fluid or blood.

Endoderm The innermost layer of cells in an embryo at the stage when the three germ layers (ectoderm, mesoderm, and endoderm) are established.

Endometrial cups Clusters of tightly packed cells from the trophoblast that become embedded deeply in the endometrium and produce eCG.

Endothelium The layer of squamous cells that line blood vessels and lymphatic vessels.

Entropy The fraction of energy that cannot be used to perform work.

Epiblast The cells that give rise to the three germ layers of the embryo (ectoderm, mesoderm, and endoderm).

Epididymis The coiled tubule attached to the testis connecting the efferent ducts with the ductus deferens. It consists of the head (caput), body (corpus), and tail (cauda).

Epithelium Avascular layer of cells that reside on a basement membrane and line all free surfaces.

Equine chorionic gonadotropin A glycoprotein hormone produced by the endometrial cups with biological activity similar to LH.

Estrus The phase of the estrous cycle during which the female is sexually receptive.

Ethics The academic discipline that deals with what is good and bad as well as what constitutes moral duty.

Excurrent ducts The system of ducts that carry fluids away from the testis.

Exocrine gland Glands that secrete materials into ducts.

External genitalia Reproductive organs located on the exterior of the body (penis and scrotum in males and clitoris and vulva in females).

Extra-embryonic membranes Membranes outside the body of the embryo involved with protection and nutrition.


Fertile Having the ability to conceive and give birth to offspring.

Fetus The unborn offspring of a viviparous animal. Typically this term is used to refer to the stage of development following implantation.

Fibroblast A star- or spindle-shaped cell with cytoplasmic processes found in connective tissue and capable of producing collagen.

Follicle-stimulating hormone A pituitary glycoprotein hormone that causes ovarian follicles to develop from the secondary to the tertiary stage.

Follicular wave The pattern of growth of tertiary follicles characterized by a rapid increase in diameter followed by ovulation or atresia.

Folliculogenesis The development, growth, and maturation of ovarian follicles.

Freemartin A sterile female born as a twin to a male with which it exchanges blood. Both the male and female twins are chimeras having a mixture of cells with XX and XY sex chromosomes.


Gametes Specialized sex cells that contain a haploid complement of chromosomes.

General moral premise A commonly held postulate regarding what constitutes moral duty or obligation.

Genital ducts The ducts of the genitals (epididymis and ductus deferens in males, and vagina, uterus, and oviducts in females).

Genital fold The bilateral creases on either side of the embryonic genital tubercle that fuse to form the shaft of the penis in males and remain separated to a cleft or vestibule of the female vagina.

Genital swelling The mound of tissue surrounding the embryonic genital folds that differentiates to form the scrotum in males and the vulva in females.

Genital tubercle The knobby prominence of the undifferentiated external genitalia that gives rise to the glans penis in males or the clitoris in females.

Germinal epithelium The layer of cuboidal epithelial cells lining the surface of the ovaries.

Gonadal dysgenesis A defect in the development of the gonads.

Gonadal ridges (Genital ridges) Knots of connective tissue superficial and medial to the embryonic kidney that will differentiate into the testes or ovaries.

Gonadotropin A hormone that promotes the growth and function of the gonads (e.g., LH and FSH).

Gonadotropin-releasing hormone (GnRH) A neurohormone consisting of 10 amino acids, produced by neurosecretory cells of the hypothalamus and released into the hypothalamic-hypophysial portal system. Its major function is to stimulate release of luteinizing hormone and follicle-stimulating hormone.

Gonads The organs that produce gametes; that is, the testes and ovaries.

Granulosa cells Epithelial cells located within the lumen of the ovarian follicles.

Gubernaculum The cord of connective tissue that develops from the embryonic mesenchyme and connects the fetal testis to the scrotum. Shortening of this structure is involved with descent of the testis into the scrotum.


Haploid Half the number of chromosomes found in somatic cells.

Hatching of the embryo Escape of the developing blastocyst from the zona pellucida.

Hermaphroditism The condition characterized by the presence of both testicular and ovarian tissues.

Hilus (hilum) Point at which nerves and vessels enter and leave an organ.

Homeostasis The set of physiologic mechanisms that act to sustain a steady-state condition in an organism.

Hormone Any biochemical that serves as an intercellular messenger.

Hypersex The process by which different organisms merge and develop a permanent symbiotic relationship.

Hypoblast The layer of cells that is situated next to the yolk sac and below the epiblast of the embryo.

Hypophysis An endocrine gland suspended from the ventral surface of the hypothalamus and embedded in the hypophysial fossa, which is a depression in the dorsal surface of the sphenoid bone. Also known as the pituitary gland.

Hypospadia Developmental defect of the penis characterized by a failure of the genital folds to fuse and which leaves a urethral opening on the ventral surface of the penis.

Hypothalamus The ventral and medial portion of the diencephalons, which forming the walls of the third ventricle and lying between the optic chiasm (anterior limit) and mammillary bodies (posterior limit).


Infertile Reversible condition of a reduced ability to reproduce.

Infundibulum Any funnel-shaped structure including the prominence at the base of the hypothalamus or enlarged portion of the anterior portion of the oviduct.

Inguinal canals Openings through the abdominal oblique muscles through which the testicular spermatic cord extends to support the testes.

Inguinal hernia Protrusion of intestine through the inguinal canal due to failure of the inguinal ring to close.

Inguinal rings The arrangement of abdominal muscle that forms the inguinal canals.

Inner cell mass A collection of compacted cells in the blastocyst, which is differentiated from the outer trophoblast. This structure will develop into the embryo.

Interphase The phase between two successive cell divisions.

Intracellular messenger Any biochemical that is generated as a result of a hormone binding to its receptor which initiates a cascade of intracellular events that influence cell function.

Intrinsic value The value of an organism that is distinct from any instrumental value it might have.

Ischiocavernosus muscle A skeletal muscle extending from the ischium to the corpus cavernosum of the penis. Contraction of this muscle compresses the crus penis.

Isthmus The narrow part of the oviduct located between the ampulla and the uterus.


Labia The lip-shaped folds of the female external genitalia. They consist of an outer labia majora, and an inner labia minora.

Large luteal cells Endocrine cells of the corpus luteum derived from granulosa cells.

Lateral To the sides away from the median or midsagittal plane.

Leptotene The early stage of meiosis during which the chromosomes shorten and appear as long, separated filaments.

Leydig cells Interstitial testicular cells that occupy the space between the seminiferous tubules and produce testosterone.

Ligaments A fold of peritoneum that suspends organs from the abdominal wall.

Lobule Small lobes. Subdivisions of an organ created by septa that extend from the surface to the deep interior.

Low-density lipoprotein A complex of molecules consisting of lipid and protein. These compounds are internalized by cells and serve as the major source of testosterone.

Lumen The interior space of a tubular structure such as the intestine, vagina, or urethra.

Luteinization Morphologic and biochemical transformation of an ovulated ovarian follicle into a corpus luteum.

Luteinizing hormone A pituitary glycoprotein hormone that stimulates development of ovarian follicles to the preovulatory stage, induces ovulation, and causes the primary oocyte to complete the first meiotic division.

Luteolysis The dissolution of the corpus luteum.


Masculinization The acquisition of masculine traits during sexual differentiation.

Medial Toward the middle or near the median or mid-sagittal plane.

Median The center, middle, or midline.

Median eminence The ventral portion of the hypothalamus that forms a mound that is continuous with the infundibulum.

Mediastinum Central mass of connective tissue in the testis, joined to the tunica albuginea by numerous projections that divide the testis into lobules.

Medulla The center of an organ.

Meiosis A type of cell division in which a cell undergoes two divisions of the nucleus and gives rise to four gametes, each of which has the haploid number of chromosomes.

Meiotic sex Reproduction that requires the fusion of male and female gametes, each of which develops from meiosis.

Mesenchyme Connective tissue of the early embryo.

Mesentery A fan-shaped fold of peritoneum that suspends the bulk of the small intestine from the abdominal wall.

Mesoderm The middle layer of cells in an embryo at the stage when the three germ layers (ectoderm, mesoderm, and endoderm) are established.

Mesonephric duct The tubule that drains from the embryonic kidney (mesonephros) to the cloaca in the embryo.

Mesonephros The early embryonic kidney that eventually regresses as the metanephric kidneys develop.

Mesothelium A single layer of squamous cells that lines serous cavities, such as the peritoneum.

Metanephros The permanent kidney that develops from the uretic buds of the embryo.

Metaphase The stage of meiosis or mitosis during which chromosomes become aligned at the equator of cell.

Metestrus The phase of the estrus cycle between estrus and diestrus, during which the corpus luteum is developing.

Microcotyledons A structure of the fetal placenta supplied with blood vessels and forming chorionic villi, which attaches to the uterine endometrium. Similar to cotyledons, only these are not visible to the naked eye.

Mitosis The process of cell division whereby one cell gives rise to two offspring cells, each of which is identical to the parent cells.

Monoestrous Exhibiting one estrous cycle each year.

Moral considerability A trait or set of traits that confer(s) moral value to an entity (e.g. the ability to reason).

Moral significance The degree of moral value conferred to an entity. For example, a dog and human may each have moral value, but one is given a higher priority in moral decision making.

Morula The stage of embryo development during which the embryo consists of a compact mass of blastomeres resembling a mulberry.

Mucosa The innermost layer of tissue in a tubular organ consisting epithelial cells, basement membrane, and in some cases a layer of smooth muscle.

Mucous membrane The layer of epithelial tissue that lines the inner walls of tubular organs.

Mullerian ducts The pair of embryonic ducts, also known as paramesonephric ducts, that give rise to the upper vagina and uterus in females.

Muscularis The muscular layer of a tubular structure (usually smooth muscle) that lies beneath the serosa. In its most developed state this layer consists of two sublayers of circular and longitudinal muscle.


Negative feedback A control mechanism whereby a response inhibits the mechanism responsible for generating it.

Nerve fiber The axon of a nerve cell.

Nerve ganglion A grouping of nerve cell bodies located outside the central nervous system.

Nerve nucleus A grouping of nerve cell bodies located within the central nervous system.

Nerve tract A bundle of parallel nerve fibers within the central nervous system.

Neuroendocrine Referring to interactions and/or interfaces between the nervous and endocrine systems.

Neurohypophysis The posterior lobe of the pituitary gland.

Neuron A nerve cell.

Neurosecretory cells A nerve cell that releases a hormone into the extracellular space.


Omentum A fold of peritoneum passing from the stomach to other viscera.

Oocyte A primitive form of the female gamete.

Oogenesis Process by which the ovum is developed.

Oogonia Primitive germ cells of the female that undergo mitotic divisions to give rise to primary oocytes.

Organizational actions Actions of steroid hormones that induce permanent changes in structure of the central nervous system.

Ostium Entrance or small opening to a hollow organ.

Ovary The female gonad.

Oviducts Narrow extensions of the uterine horns consisting of the infundibulum, ampulla, and isthmus.

Ovulation The process whereby a mature ovarian follicle ruptures to release the oocyte.

Ovulatory wave A wave of follicle growth that ends with ovulation.

Oxytocin A polypeptide hormone produced in the hypothalamus and released from the posterior pituitary gland in response to suckling or stretching of the cervix to induce milk ejection from the mammary gland or contraction of the myometrium.


Pachytene The stage of meiotic prophase during which homologous chromosomes form pairs and divide longitudinally to form two identical chromatids. During this stage each homologous pair exists as a cluster of four chromatids.

Paracrine A mode of hormone action in which a hormone is released into the extracellular space and acts locally on adjacent target cells.

Parenchyma The cells of an organ that are responsible for its function and are supported by connective tissue.

Parietal Referring to the wall of a cavity.

Penis The organ of copulation in males.

Perineum The external region between the vulva (females) or penis (males) and the anus.

Peritubular myoid cell A smooth muscle cell located along the basement membrane of the seminiferous tubules.

Pheromone A chemical substance that is secreted by one individual and perceived by and inducing some physiologic and(or) behavioral response in another individual.

Pituitary gland An endocrine gland suspended from the ventral surface of the hypothalamus embedded in the hypophysial fossa, a depression in the dorsal surface of the sphenoid bone. Also known as the hypophysis.

Placenta The organ regulating metabolic exchange between the fetal and maternal systems and consisting of both fetal and maternal components.

Placental lactogen A lactation-promoting hormone produced by the placenta.

Placentation The process by which the placenta becomes organized and attaches to the endometrium.

Placentoma The placental unit in the cotyledonary placenta consisting of the fetal caruncle attached to the maternal caruncle.

Polyandry A mating strategy in which females have more than one male mating partner.

Polyestrous A pattern of reproductive activity in which females express more than one estrous cycle in a year.

Positive feedback A control mechanism in which a response enhances the signal that induces the response.

Prepuce A fold of skin that covers the glans penis.

Primary follicle An ovarian follicle consisting of an oocyte surrounded by a layer of cuboidal follicular (granulosa) cells.

Primary oocyte An intermediate cell type in oogenesis arising from an oogonium and remaining in the first meiotic prophase until ovulation.

Primitive sex cords Columns of cells formed by proliferation and inward migration of cells from the mesonephros and coelomic epithelium. Development of the sex cords causes the genital ridges to enlarge and grow into the mesonephros.

Primordial follicle The most primitive follicle consisting of the primary oocyte surrounded by a single layer of follicular cells with a thin basement membrane.

Primordial germ cells The progenitors of gamete cells that originate in the inner lining of the yolk sac near the developing allantois and migrate from the yolk sac to the genital ridges during early embryogenesis.

Proestrus The stage of the estrous cycle during which a follicle or follicles develop to the preovulatory stage leading to estrus and ovulation.

Progestin A generic term referring to any substance that exerts the same biological actions as progesterone.

Prolactin A polypeptide hormone produced by the anterior pituitary gland that acts on the mammary gland to initiate lactation in most mammals, and sustains the corpus luteum in rodents.

Prophase The initial phase of meiosis and mitosis characterized by: contraction of chromosomes and migration of centrioles and asters toward the poles of the cell. In meiosis the process is divided into six stages: preleptotene, leptotene, zygotene, pachytene, diplotene, and diakinesis.

Prostate gland One of the accessory sex glands located at the origin of the urethra at the site where the two ductus deferens converge.

Proximal Near the point of origin of a structure.

Pseudohermaphroditism A condition in which an individual possesses the gonads of one sex, but the external genitalia of the other sex.

Pseudopregnancy The condition where the pattern of progesterone is the same as that characterizing pregnancy, but without pregnancy.

Puberty The physiologic, morphologic, and behavioral changes that occur in association with developing the ability to reproduce.


Radioimmunoassay A method for quantifying the amount of a chemical substance, involving standard amounts of the substance, a highly purified form of the substance labeled with a radioactive isotope, and antiserum that specifically binds the substance.

Receptor A cellular protein (membrane or intracellular) that binds a substance with high affinity and specificity.

Recrudesce To become active.

Recruitment The process whereby a cohort of secondary follicles develops into tertiary follicles.

Reproductive strategy The reproductive characteristics of individual members of a particular species that are a function of natural selection.

Rete testis The network of microscopic tubules located in the mediastinum into which the straight segments of the seminferous tubules empty.

Rete tubules The microscopic tubules of the rete testis.

Retractor penis muscles A bilateral pair of smooth muscles that originate on the ventral surface of the caudal vertebrae, circumvent the rectum, and insert into the penis on the lateral and ventral surfaces.

Rights Claims or entitlements that place limits on what a group (society) can do to an individual.

Rostral Toward the head.


Sagittal The direction along the anterior-posterior plane.

Sterol Carrying Protein-2 (SCP-2) An intracellular protein that interacts with the cytoskeleton to facilitate transport of cholesterol across the cytoplasm.

Scrotum The sac that houses the testis that is composed of skin and an underlying layer of smooth muscle called the tunica dartos.

Secondary follicle An ovarian follicle that consists of the primary oocyte encased in a translucent membrane, called the zona pellucida, surrounded by two or more layers of follicular cells.

Secondary sex traits Sexually differentiated traits that may facilitate sexual contact, but are not required for the production, transport, or fusion of gametes.

Selection The process whereby a particular tertiary follicle emerges from the pool of secondary follicles a few hours before other members of the cohort.

Sella turcica Literally "Turkish saddle." The depression in the dorsal surface of the sphenoid bone which houses the pituitary gland.

Semen The fluid ejaculated through the penis following sexual stimulation. It consists of sperm, testicular fluid, and secretions from the vesicular, prostate, and bulbourethral glands.

Seminiferous tubules The microscopic tubules that make up a bulk of the testicular parenchyma.

Serosa The outermost tissue layer of a visceral organ located within the abdominal or thoracic body cavities, consisting of the surface mesothelium and irregular connective tissue.

Serous membrane A thin membrane (e.g., peritoneum) that produces a serum-like fluid.

Sertoli cells Elongated cells within the seminiferous tubules that ensheath and provide support for developing sperm. These cells are joined laterally by tight junctions to form the blood-testis barrier.

Sex The genetic and phenotypic traits that distinguish between males and females.

Sex chromosomes Chromosomes (X and Y in mammals) that contain genes that are particularly important in determining whether an individual will develop ovaries or testes.

Sex determination The mechanisms that establish the sex of an individual; in particular those that establish what type of gonad forms during early embryogenesis.

Sexual differentiation The process by which sexually dimorphic tissues take on the male or female characteristics.

Sexual reproduction A method of reproduction in which genes from separate sources are recombined.

Sexuality A characteristic describing the sexual feelings and behaviors of an individual.

Sigmoid flexure The S-shaped curve of the fibro-elastic penis when retracted.

Small luteal cells Hormone-producing cells of the corpus luteum that are derived from theca interna cells of the follicle.

Social contract A hypothetical agreement among individuals forming a society that defines the rights and duties of individuals.

Spermatic cord A band of connective tissue that extends from the abdominal cavity through the inguinal rings and supports the ductus deferens, lymphatics, nerves, and blood vessels that carry blood to and from the testes.

Spermatids Haploid cells that metamorphose into spermatozoa and are derived from secondary spermatocytes.

Spermatocytes Parent cells of spermatids derived from spermatogonia.

Spermatogenesis The process by which spermatozoa are produced from spermatogonia.

Spermatogonia Testicular stem cells that occupy the basal region of the seminiferous tubules and differentiate into spermatozoa.

Spermatozoon The male gamete cell (also called a sperm).

Spermiation The release of spermatozoa from the apical portion of the Sertoli cells into the lumen of the seminiferous tubules.

Spermiogenesis The process by which spermatids are transformed into spermatozoa.

Spindle The fusiform structure consisting of longitudinally-arranged microtubules that appears in a dividing cell and provides tracks along which chromosomes migrate to opposite poles of the cell.

Sex Determining Region of the Y Chromosome (SRY) A gene that acts as a switch to initiate expression of other genes that direct development of the male gonad.

Steroidogenic Acute Regulatory Protein (StAR) An intracellular protein believed to play a role in transporting cholesterol molecules from the outer mitochondrial membrane to the inner mitochondrial membrane where it encounters the side-chain cleavage enzyme.

Stigma A visible spot on the surface of a mature ovarian follicle marking the point at which the membrane will rupture causing ovulation.

Stroma The portion of an organ made up primarily of connective tissue (distinguished from the parenchyma).

Submucosa The layer of connective tissue directly beneath the mucosal epithelium of a tubular organ.

Superficial Near the surface.

Superovulation A hormone treatment inducing the ovulation of more than one follicle.

Syncytiotrophoblast The outer layer of the trophoblast.

Syngamy The process by which a sperm and oocyte conjugate.


Telophase The final stage of cell division during which the spindle disappears and two nuclei appear.

Tertiary follicle An ovarian follicle with a fluid-filled antrum consisting of an oocyte, distinct granulosal, and thecal layers of follicular cells.

Testes The male gonads.

Theca A layer of follicular cells lying outside the wall of the follicle. The layer consists of an inner theca interna and outer theca externa.

Totipotent Relating to the ability of a single cell to differentiate into any cell type, and therefore develop into part of or an entire organism.

Trabeculae A meshwork of bundles of connective tissue that originate in the capsule and traverse the body of an organ.

Transgenic sex The exchange of genetic material between organisms (e.g., conjugation in bacteria).

Transverse The plane which lies across the long axis of a body.

Trophectoderm Outermost layer of cells in the blastocysts that will give rise to the trophoblast.

Trophoblast The outermost layer of cells in the blastocyst that become the fetal portion of the placenta (i.e., the chorion).

Tuberohypophysial tract A bundle of axons emanating from neuron cell bodies in the hypothalamus and terminating in the posterior pituitary gland.

Tuberoinfundibular tract Bundle of axons emanating from neuron cell bodies in the hypothalamus and terminating in the infundibulum.

Tubulus contortus The convoluted portion of a seminiferous tubule.

Tubulus rectus The straight portion of a seminiferous tubule.

Tunica albuginea Collagenous capsule enveloping the testis and ovary.

Tunica vaginalis Serous membrane (derived from peritoneum) that envelopes the testis and epididymis.


Urachus The urinary canal of the embryo emptying into the allantois.

Urethra The tubular canal running from the bladder to the exterior.

Urogenital sinus An embryonic chamber common to the reproductive, urinary, and excretory systems. Also called the cloaca.

Uterus The womb. A hollow portion of the reproductive tract where the fetus implants and develops.

Utilitarian theory An ethical theory based on the assumption that right action is that which promotes the most pleasure.


Vagina The female organ of copulation extending from the uterus to the vulva.

Vaginal cavity The space formed between the visceral and parietal tunica vaginalis once the testes have descended.

Vaginal process The cavity that forms between the visceral and parietal tunica vaginalis during testicular descent.

Vaginal tunic The tunica vaginalis.

Ventral The undersurface of an animal.

Ventricle A cavity within the brain or heart.

Vesicular glands A pair of male accessory sex glands situated laterally to the ductus deferens and dorsal to the pelvic urethra.

Vestibule The small cavity located at the entry to the vagina.

Villi Folds of tissue in a tubular organ that project into the lumen.

Visceral Referring to the viscera; that is, internal organs.

Vitelline block Biochemical changes in the oocyte that prevent more than one sperm from binding to the vitelline (oocyte) membrane.

Vulva External genitalia of the female including the clitoris, labia majora and minora, and vestibule.


Whitten effect A phenomenon in which the estrous cycles of female mice kept in a group and isolated from males will become synchronized following exposure to a male mouse.

Wolffian ducts The embryonic ducts that develop into the epididymis and ductus deferens. Also called the mesonephric ducts.


Yolk sac An extraembryonic membrane which is largely vestigial in eutherian mammals, serving only as a source of nutrients before the placenta develops.


Zona bock Biochemical changes in the oocyte that prevent more than one sperm from binding to the zona pellucida, thereby preventing polyspermy.

Zona pellucida A glycoprotein membrane surrounding the oocyte.

Zygote The diploid cell that forms upon union of a sperm with an oocyte.

Zygotene The stage of meiotic prophase during which the pairing of homologous chromosomes begins.

Keith K. Schillo, PhD

Department of Animal and Food Sciences

University of Kentucky

Lexington, Kentucky
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Author:Schillo, Keith K.
Publication:Reproductive Physiology of Mammals, From Farm to Field and Beyond
Article Type:Glossary
Geographic Code:1USA
Date:Jan 1, 2009
Previous Article:Chapter 18: Ethical issues in reproductive physiology.

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